A heap overflow in the FSViewer.exe process of FastStone Image Viewer v8.3 allows an attacker to supply a crafted JPEG 2000 (JP2) file and cause execution of arbitrary code in the context of the current process. The vulnerability is a classic buffer overflow on the heap and would let the attacker run malicious code with the same permissions as the user opening the image, potentially compromising confidentiality, integrity, and availability of the affected system.

FastStone Image Viewer version 8.3 is the only affected product listed. No additional releases or vendors are mentioned, indicating the flaw is confined to this specific product and version.

The EPSS score is not available and the vulnerability is not listed in the CISA KEV catalog, suggesting the current exploitation risk is low but not impossible. The attack vector requires user interaction with a malicious JP2 file; an attacker must entice a user to open the crafted image. If exploited, the flaw would provide high‑severity arbitrary code execution with user privileges. Until an official patch or update is released, the risk remains moderate due to the need for a crafted file and user action.